1. Field of the Invention
The present invention relates generally to composite tubing and methods for fabricating composite tube structures having integrally-formed tapered ends. More particularly, the present invention relates to a method for fabricating composite tubes having clevis connectors at one or both ends.
Reinforced composite tubing is useful for many purposes including the construction of structural frameworks. Desirably, such structural tubing will possess high tensile and compression strength, even at high and low temperature extremes, as well as high specific strength, rigidity, and modulus. Advanced composites have particularly favorable high strength to density ratios and are especially attractive for space applications, where high strength and low weight are important.
While great progress has been made in the fabrication of the composite tubular members themselves, the strength of any structure formed from the tubes depends ultimately on the ability to make high strength connections between individual tube members. It would be desirable, for example, to provide end connectors on individual tube members which approach or exceed the strength in the remainder of the tube. In particular, it would be desirable to provide tubes which have smooth transitions at each end into various tapered connector configurations, such as clevises tangs, and the like. Such tapered end connectors will tend to uniformly distribute stress into the main portion of the structural member. Moreover, the tapered end regions can be locally reinforced in order to reduce the chance of failure within the transition regions.
The use of composite tubular elements having tapered structural end connectors is described generally in U.S. Pat. No. 4,963,301, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. The composite tubular element which is illustrated in FIG. 3 of the '301 patent incorporates many of the advantages just discussed, but suffers from a region of weakness in the joint or seam which is formed between the primary cylindrical portion 52 and the separately formed tapered end 60. Composite structural members of the type illustrated in the '301 patent would possess superior strength characteristics if they could be formed as an integral structure substantially free from seams and joints.
The manufacturing method described in U.S. Pat. No. 4,963,301, however, does not permit the formation of composite tubular elements which are tapered at both ends. As the composite tubes are formed and cured over a solid mandrel, the tapering of both ends would prevent removal of the mandrel after the tube is finished.
It would therefore be desirable to provide methods for forming reinforced composite tubing elements having integral tapered ends. In particular, it would be desirable to provide methods for forming such tubes over a mandrel and for removing the mandrel prior to curing of the composite matrix material. The method should provide reinforced composite tubing elements having integral end connectors, such as clevises and tangs, where the connectors are formed as continuous extensions of the fabric reinforcement material and the entire tube is substantially seamless and free from joints, junctures, and the like.
2. Description of the Background Art
U.S. Pat. No. 4,963,301 has been described above. U.S. Pat. Nos. 4,983,422; 4,837,230; and 4,741,873, assigned to the assignee of the present invention, each describe methods for forming refractory composite materials which may be employed in forming the composite tubes of the present invention. The disclosures of these three patents are incorporated herein by reference.
U.S. Pat. No. 4,397,048, describes the use of an inflatable mandrel to produce an artificial limb component having an expanded size clevis at one end. U.S. Pat. Nos. 4,126,659; 3,833,699; 3,258,384; and 2,967,796, teach the use of clamshell molds in combination with an inflatable mandrel to produce molded products. U.S. Pat. No. 4,902,458, describes a method for molding hollow bicycle frame components. U.S. Pat. No. 4,900,487, describes a method for molding hollow plastic objects. U.S. Pat. No. 2,456,513, describes a collapsible skeleton structure and a flexible bag for molding processes.